At the heart of Africa lie the Virungas, a chain of volcanoes that are home to the last of the mountain gorillas. Every few years one of the Virungas erupts, dribbling lava down its misty slopes, torching the bamboo thickets where the gorillas live and burying villages and farms. These local disasters are dwarfed by the greater cataclysm to come. The craters of the Virungas are fiery peepholes into a tectonic fissure – the Great Rift – that will one day slice Africa in two from the Red Sea down to Mozambique. Seen from 10,000ft up under a crater’s lip, the distinct characters of these two future Africas are already apparent. To the west, spreading lazily down to the Atlantic, are a thousand miles of jungle, the canopy rolled flat by low, lumbering rain-clouds. To the east is high, rocky savannah: cool, grassy, blessedly free of mosquitoes and running clear over several dusty horizons before plunging into the Indian Ocean.

A continental split happens in a two-step process of violence. First, as the earth’s plates move apart, they stretch the land’s surface so thin that lava from the earth’s core bursts through, then settles in monstrous pustules of cooling ash and rock. Then as the partition widens further, the cones collapse and form a depression that, when the last one falls, fills with angry, hissing sea.

On a continental scale, this division proceeds slowly. Africa’s rift is widening at the same speed as a fingernail grows, and a process that began 100 million years ago will take at least another 10 million to complete. Up close, however, the separation can be dramatic. In 2002, the largest Virunga, Mount Nyiragongo, spat a river of lava into Goma, carving Congo’s second city in two with the loss of 147 lives. Three years later, Ethiopian villagers watched helplessly as their camels tumbled into a crack eight meters wide and 36 miles long that opened in the earth in just 10 days, the animals’ bellows rising to shrieks as they hit the white-hot sludge bubbling up in its trough.

After seven years in Africa, I came to see the continent’s eventual geographic destiny as a metaphor for its more immediate human one. There is always violence. But inexorably the land rises. Then finally it breaks free.